Brushless direct current motor



May 28, 1968 R. K. HILL BRUSHLESS DIRECT CURRENT MOTOR 2 Sheets-Sheet 1Original Filed Oct. 8, 1962 IN VEN TOR. F0) 4 R. K. HILL 3,386,019

May 28, 1968 BRUSHLESS DIRECT CURRENT MOTOR 2 Sheets-Sheet 2 OriginalFiled Oct. 8,

ac. Pom/2 INPUT R2 I I I I 6 G Q44 0&- Q-3a (M4 4 1%. 42-41 P4 [0 "f 1;E1 (5 D \I i Od O-J Q16 04k Q-Zb 0-3; m 3

q l l l l l INVENTOR. Z5 #07 4 H/LZ United States Patent 2 Claims. (Cl.318-138) ABSTRACT OF THE DISCLOSURE A D.C. powered motor is providedwith a brushless commutating means including a rotatable L-shapedmagnetic member having one leg extending along the axis of rotation forthe magnetic member. Such leg also extends through the center of asingle coil having an A.C. signal impressed thereon so that for allangular positions of the magnetic member coupling between such memberand the coil is uniform. The other leg of the magnetic member sweeps infront of a circular array of pole faces to induce switching signals inindividual pickup coils associated with the individual pole faces. Theaforesaid pole faces are disposed at the ends of stationary pole pieceseach having an individual one of the pickup coils coupled thereto. Otherends of the stationary pole pieces are positioned in uniform magneticcoupling relation to the first recited leg of the rotatable magneticmember for all positions of the latter.

This application is a division of copending application Serial No.228,849 filed October 8, 1962, relating to direct current, energizedmotors in general, and more particularly relating to a motor having theoperating characteristics of a conventional D.C. motor; yet isconstructed so that commutation takes place without utilizing wearingsurfaces, sliding surfaces, separable contacts or contact devices havingrelatively movable parts which physically engage one another.

In a conventional direct current machine, commutation is essentially amechanical switching operation by which currents through the variousarmature conductors are cyclically reversed in sequence as a function ofrotor position. This continuous switching process is accomplished bymeans of brushes and a segmented commutator so that commutation isunavoidably accompanied by friction wear, and sparking with itsattendant generation of RF. noise. These disadvantages of commutationfrequently prohibit the utilization of D.C. motors in criticalapplications even though the performance characteristics and inputrequirements favor the use of a D.C. motor in all other respects.

The prior art has produced a number of brushless D.C. machines, but itis believed that none of the prior art devices provide the performancecharacteristics of a conventional commutation D.C. machine. That is,these machines either convert direct current to alternating current toeffectively provide an A.C. motor or else rotor velocity is employed forswitching control. In either event, the result is not a duplication ofdirect current motor performance. The instant invention provides a D.C.motor having the desirable characteristics of a conventional commutatingmachine, but does not require relatively moving parts in physicalengagement in order to achieve commutation. Further, rotor position isdetectible even with the machine at standstill so that current switchingcontrol is independent of rotor velocity.

In one embodiment of the instant invention, conventional commutation issimulated by an optical sensing system in conjunction with an electronicswitching net- 3,386,019 Patented May 28, 1968 work. This opticalelectronic system is capable of reversing and advancing armaturecurrents in sequence as a function of rotor position. The motor utilizesa permanent magnet rotor for field excitation in combination with astator comprising conventional D.C. armature windings.

A light source fixed to the motor frame has the beam thereof directedthrough an aperture in a shield carried by the rotor and rotatabletherewith. The light beam passing through the shield aperture impingesupon a least one of a number of photoelectric devices spaced around theshield so that as the rotor rotates, the light beam scans thephotoelectric devices in sequence. As the photoelectric devices areilluminated, the impedance level of a circuit controlled thereby islowered so that it acts as a closed switch permitting current to passthrough appropriate stator windings in the appropriate direction.

The number of photoelectric devices provided is equal to the number ofcom-mutator bars which would normally be required for a similar armaturewinding of a conventional D.C. machine. As the rotor rotates, aparticular photoelectric device is illuminated causing particulararmature windings to be energized. The energized windings are positionedso that the magnetic fields generated thereby cooperate with the fieldof the permanent magnet to cause rotation of the rotor in the requireddirection.

Accordingly, a primary object of the instant invention is to provide anovel construction for a brushless D.C. machine.

Another object is to provide a brushless D.C. machine having thecharacteristics of a conventional commutating D.C. machine in thatcurrent flows through all sections of the stator winding forsubstantially all rotor positions.

Still another object is to provide means whereby a sequence ofelectrical signals are determined by rotor position independent of rotorspeed.

A still further object is to provide a D.C. machine in which commutationis achieved by electronic switching means without the necessity ofuitlizing relatively moving parts which physically engage one another.

A still further object is to provide a D.C. motor in which commutationis achieved by means of a rotating magnetic member extending from asingle coil which generates a signal that is distributed in sequence topickup coils arranged in a circular array.

Yet another object is to provide a D.C. machine in which switchingsignals are coupled to the commutating device by means of a field actingthrough an air gap.

These as well as other objects of this invention shall become readilyapparent after reading the following description of the accompaningdrawings in which:

FIGURE 1 is a perspective of a brushless D.C. machine constructed inaccordance with the teachings of the instant invention.

FIGURE 2 is an exploded perspective of the machine of FIGURE 1.

FIGURE 3 is a schematic representation of the rotor position detectingportion of the motor illustrated in FIGURES 1 and 2.

FIGURE 4 is a schematic illustrating the stator windings and theirconnections to the DC. energizing source through the electronicswitching devices typically illustrated in FIGURE 5.

FIGURE 5 is a schematic illustrating one of the six photoelectricswitching units of FIGURE 4.

FIGURE 6 is a schematic of another embodiment of this invention in whichswitching signals are magnetically coupled to the commutating devices.

FIGURE 7 is a cross-section taken through line 7-7 of FIGURE 6 lookingin the direction of arrows 77 with certain elements removed for the sakeof clarity.

Now referring to FIGURES 1-5 and more particularly to FIGURE 2.Brushless DC. motor comprises shell 11 which surrounds stationaryarmature assembly 30. The ends of shell 11 are covered by front and backend caps 13, 14, respectively, each provided with suitable bearings 15which rotatably support motor shaft 16. Rotor 17 is a permanent magnetkeyed to shaft 16 and disposed within armature assembly 30.

Stationary armature assembly 30 includes relatively low reluctancemagnetic member 29 which is laminated and provided with teeth and slotswherein winding 12 is disposed and held by shell 11. Winding 12 consistsof a conductor threading the slots of magnetic member 29 a plurality oftimes and finally joining the starting point in a closed loop (seeFIGURE 5). A plurality of equally spaced taps or junction points 41through 46 divide winding 12 into six sections or coil portions 31through 36.

Commutation is achieved by means of solid state power switching unit 18and solid state control and preamplifier unit 19 controlled by lightsource 20 and shield 21. Units 18 and 19 are mounted to the rear of endcap 14 being operatively positioned by means of appropriate spacers 27,28. Preamplifier unit 19 includes a plurality of photoelectric devicesP1 through P6 equally spaced from one another and circularly arrangedabout shield 21.

Light source 20 is mounted to power switching unit 18 on the forwardside thereof and extends through central aperture 22 of preamplifierunit 19 into the interior of shield 21. Shield 21 is keyed to motorshaft 16 and is disposed rearwardly of end cap 14 extending throughaperture 22. Shield 21 is provided with an aperture 23 so positioned andshaped that light emanating from source 20 and passing through aperture23 will impinge upon at least one of the photoelectric devices P-lthrough P6 for any position of rotor 17.

Cover 24 is provided as an enclosure for the elements to the rear of endcap 14. An appropriate aperture not shown is provided through cover 24to permit the passage of leads 25, 26 for connecting motor 10 to asource of direct current.

FIGURE 5 illustrates the current conditions through armature 12 whenphotoelectric device P1 is illuminated, as will be more fully explainedhereinafter. At this time, winding junctures 41 and 44 are essentiallyconnected directly to leads 25, 26 which in turn are connected to thenegative and positive terminals of a DC. power source. Under thesecircumstances, two parallel current paths exist between junctures 41 and44. One path consists of windings 34, 35, 36 connected in series and theother path consists of windings 33, 32, 31 connected in series.

Photoelectric device Pl is of a type well-known to the art whichpossesses two states of conduction. That is, low conductance or highimpedance when not illuminated and high conductance or low impedancewhen illuminated. Since the position of rotor 17 determines the positionof shield slit 23, the position of rotor 17 determines whether or not P1is illuminated.

When Pl is illuminated there is a relatively low impedance current pathfrom lead through the emitter to base junction of NPN type transistorQ8, through the emitter to base junction of NPN type transistor Q7through resistor R-1 and Pl to lead 26. This emitter to base current ofQ7 is suflicient to create a low impedance path from emitter tocollector of Q7. Consequently, a second larger current flow in the nowrelatively low impedance path from lead 25 through the emitter to basejunction of Q-8, from the emitter to collector of Q7 through R7, throughthe base to emitter junction of PNP type transistor Q9 to lead 26.

When this second current flows a low impedance condition is created fromthe emitter to collector of Q8 and from the collector to emitter of Q9.A third and still larger current flows through the now relatively lowimpedance path from lead 25 to the emitter Q-8, from the emitter tocollector of QS, from the base to emitter junction of PNP typetransistor Qla, through the windings of armature 11 from juncture 41 tojuncture 44 through the emitter to base of NPN type transistor Qlb,thence from the collector to emitter of Q9 to lead 26.

A fourth and still larger current flows in the now relatively lowimpedance path from lead 25, from collector to emitter of QIa, througharmature 11 between juncture 41 and 44, thence from emitter to collectorof Qlb to lead 26.

These four current paths drop in impedance in a raid almostinstantaneous sequence with a switching time in the order ofmicroseconds which is an insignificant portion of the conducting timefor photoelectric device Pl.

R-1 and R-2 are connected between photoelectric device P1 and lead 25with the juncture between these resistors being connected to the base ofQ7. Resistor R5 is connected between the emitter of Q7 and lead 25 whileresistor R-S is connected between the base of Q9 and lead 26. Resistor,R7 is connected between collector of Q7 and base of Q9. Resistor R4 isconnected between the emitter and base of Qlb while resistor R6 isconnected between the emitter and base of Q-1a. The purpose of R-2through R6 is a well known and practiced art. They offer betterstabilization of the associated transistors by shunting some of thetransistors leakage current around the base-emitter junction.

The current between junctures 41 and 44 produces a magnetic fluxoriented to be essentially in spaced quadrature with the flux of rotor17. When rotor 17 is rotated for 360 divided by the number of switchinglegs used, in this case six, shield 21 is advanced so that lightdirected through aperture 23 illuminates photoelectric device P-2 of acircuit identical to that of FIGURE 5. However, as seen in FIGURE 4,this circuit connects the armature windings so that current now flows intwo parallel paths between junctures 42 and 45. Aperture 23 is wideenough to always illuminate at least one of the photoelectric devices P2through P6 with a small overlap. This is typical of commutation inconventional D.C. machines and assures that armature 11 will beenergized on starting for all positions of shaft 16.

As should now be apparent, there are siX different circuits identical tothat of FIGURE 5. Essentially, only one of these circuits is active atany given time. It is the active circuit which determines the currentpath through the windings of armature 11. This arrangement isschematically illustrated in FIGURE 4. As seen from the description ofFIGURE 5, Qla and Q-lb conduct simultaneously. Similarly there is asimultaneous conduction of transistors Q-Za and QZb, simultaneousconduction of Q-3a and Q-3b, and so on.

To insure deep saturation of transistors Qla and Qlb, an alternateconnection can be made. The emitter of Q9 can be connected to the baseof PNP transistor, Q-la and the emitter of Q-S can be connected to thebase of NPN transistor, Qlb, the collector of Q-9 being connecteddirectly to juncture 45 and the collector of Q8 being connected directlyto juncture 42. The collector of Qlb can be connected to juncture 41 andthe emitter of Q-lb can be connected to line 25 with the collector ofQ-la being connected to juncture 44 and the emitter of Q-la beingconnected to line 26. Resistors R-4 and R6 can be connected betweenemitter and base of transistors Qla and Qlb, respectively.

FIGURES 6 and 7 illustrate another embodiment of this invention in whichmotor shaft 71 carries L-shaped member 72 constructed of magneticmaterial. Leg 73 of member 72 extends from one end of shaft 71 along theaxis thereof while the other leg 74 is of fan shape and is positioned tosweep past a number of circularly arranged L-shaped pole pieces 81through 86. Individual secondary windings 91 through 96 are provided forpole pieces 81 through 86, respectively. A single primary winding 87surrounds leg 73 of member 72. One of the pole faces of each of the polepieces 81 through 86 is positioned in magnetic coupling relationship toleg 73. The other pole faces of members 81 through 86 are circularlyarranged and are positioned so that as shaft 71 rotates, leg 74 ofmember 72 will at all times be in magnetic coupling relationship with atleast one of these latter mentioned pole pieces.

With the elements in the position of FIGURES 6 and 7, it is seen thatleg 74 partly overlies the pole faces of pole pieces 81 and 82. Underthese circumstances, two relatively low reluctance paths exist. Onecomprising member 72 and pole piece 81 and the other comprising member72 and pole piece 82. A signal from an electronic oscillator (not shown)is introduced at terminals 97, 98 of primary 87 with this oscillatorsignal being coupled to secondary windings 91 and 92. At this time,there is no output from secondary windings 93 through 96. The signalsintroduced in the secondary windings may be used directly to eliectswitching operations or may be converted to a DC. signal by elements 77through 79 in the illustration of FIGURE 6.

Thus, it is seen that the instant invention provides a novelconstruction for a dire-ct current machine having the characteristics ofa typical D.C. machine with brush type commutating means. Theconstruction is such that all relatively moving commutating elements arephysical-1y spaced from each other so that switching signals are coupledthrough an air gap. Further, the construction is such that rotorposition is detectib'le even with the rotor at standstill.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now be apparent tothose skilled in the art. Therefore, this invention is to be limited,not by the specific disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1. A device of the class described comprising a torque producing unit, aswitching means and control means. for operating said switching means;said unit including a rotor and a stator; said switching meansoperatively connected to said stator for controlling energizationthereof; said control means including a portion mounted for rotation bysaid rotor; said portion being physically spaced from said switchingmeans and operatively positioned to control operation thereof wherebypredetermined parts of said stator are energized in accordance withrotor position; said switching means compising a plurality of secondarycoils and a plurality of stationary pole pieces, one for each of saidsecondary coils; said pole pieces arranged so that a first pole face ofeach constitute a circular array; said portion comprising a rotatablepole piece; said control means including a primary coil positioned inuniform magnetic eouplng relation with said rotatable pole piece for allangular positions thereof; for any position of said rotor, saidrotatable pole piece cooperating with at least one said stationary polepiece to form a relatively low reluctance path whereby A.C. signals impressed upon said primary coil will be coupled through said rotatablepole piece to the particular secondary coil associated with the lowreluctance path; said rotatable pole piece being generally L-shaped withone leg thereof positioned along the rotational axis of said rotor inmagnetic coupling relationship with said prmary coil; the other leg ofsaid rotatable pole piece being in magnetic coupling relationship with adifferent one of said first pole faces for diiierent positions of saidrotor; said one leg extending into said primary coil; and the other legof said rotatable pole piece being generally fan-shaped with the sideboundaries diverging as they move away from said rotational axis.

2. A device of the class described comprising a torque producing unit, aswitching means and control means for operating said switching means;said unit including a rotor and a stator; said switching meansoperatively connected to said stator for controlling energizationthereof; said control means including a portion mounted for rotation bysaid rotor; said portion being physically spaced from said switchingmeans and operatively positioned to control operation thereof wherebypredetermined parts of said stator are energized in accordance withrotor position; said switching means comprising a plurality of secondarycoils and a plurality of stationary pole pieces, one for each of saidsecondary coils; s-aid pole pieces arranged so that a first pole face ofeach constitute a circular array; said portion comprising a rotatablepole piece; said control means including a primary coil positioned inuniform magnetic coupling relation with said rotatable pole pece for allangular positions thereof; for any position of said rotor, saidrotatable pole piece cooperating with at least one said stationary polepiece to form a relatively low reluctance path whereby A.C. signalsimpressed upon said primary coil will be coupled through said rotatablepo-le piece to the particular secondary coil associated with the lowreluctance path; said rotatable pole piece being generally L-shaped, oneleg of said rotatable pole piece positioned along the rotational axis ofsaid rotor and extending into said primary coil for all angularpositions of said rotor; said one leg positioned in uniform magneticcoupling relationship to a second pole face of each of said stationarypole pieces; the other leg of said rotatable pole piece being inmagnetic coupling relationship with a different one of said first polefaces for different positions of said rotor; said one leg of therotatable pole piece being positioned along the rotational axis for saidrotatable pole piece and the other leg extends in a plane generallyperpendicular to said rotational axis for said rotatable pole piece;said other leg being fan-shaped with side boundaries diverging as theymove away from the rotational axis for said rotatable pole piece; saidother leg being proportioned so that for any given angular position ofsaid rotatable pole piece the other leg is in magnetic couplingrelationship with at least one and no more than two of said pole faces.

References Cited UNITED STATES PATENTS 2,980,839 4/ 1961 Haeus'sermann318-254 X 3,091,728 5/1963 Hogan et al. 318-138 ORIS L. RADER, PrimaryExaminer. G. SIMMONS, Assistant Examiner.

